The issues with casting against nearby moving targets apply to more than just Legacy controls. If an enemy passes through my hitbox, requiring a 180* or so turn, I cannot humanly hit Face Target quickly or frequently enough to prevent immediately interruption. Luckily, aiming the camera manually gives a little over a half second to re-aim before automatically cancelling the cast, which is what I'm then forced to use in these situations.
More broadly on topic:
This may be wishful thinking, but it sounds to me like we'll simply be playing with constant Face Target being active whenever we're stationary. Without that, I don't see how Dragon's Gaze or Doom eye mechanics, etc., would be an issue, if those were also mentioned. (I only remember hearing Blighted Bouquet mentioned in the LL, which I thought was triggered by performing any action, including movement or character turning, during the cast.) What I worry about is any lost functionality of the Auto-Face feature, imperative especially to attacking while moving out of a hitbox or away or at strafe from the target (usually mid-jump with the camera held down in my case, to prevent auto-turning). Even if I were the most avid of PvPers, vastly tired of seeing WARs auto-parry attacks from all sides during Raw Intuition even while running backwards (facing you and running away without the backpedaling speed penalty) via hardware macros, it wouldn't make up for what I'd be losing everywhere else — assuming PvP itself would still feel playable on my melee with latency already requiring use of mid-jump auto-faced attacks just to score a hit on someone running within my hitbox as a melee...
If everything somehow works out, I feel like this could be a nice aesthetic bonus. My ranged attacks will no longer be awkwardly facing away from the enemy during movement (or at any time I'm not spamming Face Target, really). But I can't help but think that if Face Target simply weren't automatically cancelled by any other action (except movement facing out of the 75 or so degrees to either side of the target) and a small internal cooldown were added to the Face Target command to prevent Facing 'exploits' in PvP, this could have been solved a lot more easily.